The present invention relates to a ferro fluidic seal, or a magnetic fluidic seal. The present seal is used as a dust seal, a vacuum seal, or a seal for a nuclear application apparatus for confining radioactivity. With the use of a ferro fluidic seal, a high density magnetic disc memory with a flying head which flies 0.22-0.27 .mu.m height may be implemented.
A ferro fluid is a liquid having ferro-magnetic property, and said ferro fluid is composed of carrier fluid, magnetic particles in that fluid, and stabilizer or interface activator which holds magnetic particles in a colloidal status. Since magnetic particles are in colloidal status, those particles are distributed uniformly in fluid, but do not couple with one another.
A ferro fluidic seal is used in a magnetic flux, and the sealing capability (allowable pressure) is proportional to the product of the magnetic flux and the magnetic field in the fluid. A ferro fluidic seal has the advantages that a complete seal is accomplished with small friction, a complete seal with no leak is obtained, and the manufacturing accuracy of a spindle and/or a bearing needs not be so severe.
Since ferro fluid is worn or exhausted in a long run due to evaporation et al of the fluid, fresh fluid must be supplied. Fresh fluid may be supplied either from an external member outside of a seal, or an inner member within a seal. Usually, an inner supply means is used because of the simplicity of the structure of a seal.
FIG. 1 shows the structure of a fragmentary perspective view of a prior ferro fluidic seal which seals a spindle passing through a housing. In FIG. 1, the reference numeral 1 is a housing, through which the spindle 2 passes. The seal comprising a pair of ferro-magnetic yoke rings 4a and 4b, a permanent magnet 3 positioned between said yokes, and a fresh fluid storage 6 which contains ferro fluid, is positioned between the spindle 2 and the housing 1. The seal is fixed to the housing 1 by using adhesive means or O-ring seal. In the above structure, a magnetic flux passes from the magnet 3, through the yoke 4a, the spindle 2, and the yoke 4b, to the magnet 3, and the ferro fluid 5 in the gap between the spindle 2 and the yokes 4a, 4b provides the complete seal.
Fresh fluid is supplied from the fresh fluid storage 6 to said gap, as the fluid is exhausted. In a prior art, said fresh fluid storage 6 is a porous sintered metal, porous plastics, or felt. The U.S. Pat. No. 3,740,060 discloses a shaft seal with porous fluid reservoir.
However, a porous metal has the disadvantages that the manufacturing process of that metal is complicated, and as the metal must be fixed to the yokes 4a and 4b through adhesive means, the assembling process is complicated as well. A porous plastics has the disadvantages that the accurate manufacturing is difficult, and if the accuracy is not sufficient, the trouble that the fresh fluid storage 6 might contact with the spindle 2 occurs. Further, a felt for use as a fresh fluid storage has the disadvantages that accurate manufacturing is complicated, and a fiber separated from the felt body stains a spindle and/or a bearing.